Seven lamps were placed at the top of the seven branches. Oil and wicks were placed in these lamps. The six lamps faced the "western lamp." There are various opinions regarding this expression. Some maintain that the middle lamp faced west toward the Holy of Holies, the resting place of the Ark of the Covenant. All through the era that the High Priest Shimon HaTzaddik (Simeon the Righteous - at the beginning of the Second Temple period) was alive, the western lamp was never extinguished. "This was testimony to all that the Divine Presence dwelled in Israel." (Source:Menahot 86). 
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Contents:   Part I,    Part II,    Part III,    Part IV,    Part V,    Part VI,    Part VII